We are continuing to make progress in our goal of defining germline modifiers of tumor progression and metastasis in prostate cancer. First, we are utilizing the well characterized C57BL/6-Tg(TRAMP)8247Ng/J (TRAMP) mouse model of aggressive neuroendocrine prostate cancer to investigate the role of hereditary factors in the development of aggressive disease with associated neuroendocrine differentiation (NED). We have conclusively proven that the introduction of germline polymorphism into this model by breeding significantly modulates tumor progression and metastasis. Specifically, we have approached this by crossing TRAMP mice to the eight progenitor strains of the Collaborative Cross (CC) RI panel. We have observed profound differences in tumor burden and metastasis frequencies in each of the TRAMP x CC progenitor F1 strains. In the last year, we have used this earlier work to direct F2 intercross experiments between the TRAMP mouse and CC progenitor strains that displayed the greatest differences in tumor progression and metastasis compared to the wildtype TRAMP mouse. Specifically, we have completed intercrosses between the TRAMP mouse and three CC progenitor strains: NOD/LtJ, which displays accelerated tumorigenesis and metastasis compared to wildtype mice; PWK/PhJ, which displays almost complete suppression of neuroendocrine tumor growth; and WSB/EiJ, which displays a high metastatic potential in spite of suppressed tumorigenesis. Analysis and fine mapping of tumor progression and metastasis quantitative trait loci (QTLs) is ongoing. In addition to these F2 intercross experiments we are in the process of performing or plan to initiate QTL mapping experiments in the TRAMP mouse using advanced mapping panels in the next year. Mapping panels utilized include Diversity Outbred (DO) mice and the Collaborative Cross (CC). We are also in the process of developing novel mouse models of prostate cancer since the molecular and histological features of TRAMP tumors are rather different from those observed in human prostate cancer. The ongoing aim here is to develop an animal model that more faithfully recapitulates the molecular events that lead to the initiation of tumorigenesis in human prostate cancer. Specifically, transgenic mice are being generated that over-expresses various combinations of oncogenes and micro-RNAs (miRNAs) targeting genes that are dysregulated in the early stages of prostate tumorigenesis. We have generated four transgenic mouse strains expressing a variety of miRNAs and oncogenes driven from prostate-specific promoters. Aging and characterization of these strains is ongoing, with the aim being to identify the transgenic strain displaying the most robust tumorigenesis and metastasis. Once said strain is identified, we plan to perform the same QTL mapping experiments as were done with the TRAMP mouse using the DO and CC advanced mapping panels.